Oxygen-17 anomaly in soil nitrate: A new precipitation proxy for desert landscapes

Abstract

The nitrogen cycle in desert soil ecosystems is particularly sensitive to changes in precipitation, even of relatively small magnitude and short duration, because it is already under water stress. This suggests that desert soils may have preserved past evidence of small variations in continental precipitation. We have measured nitrate (NO3−) concentrations in soils from the Atacama (Chile), Kumtag (China), Mojave (US), and Thar (India) deserts, and stable nitrogen and oxygen isotope (15N, 17O, and 18O) abundances of the soil NO3−. 17O anomalies (Δ17O), the deviations from the mass-independent isotopic fractionation, were detected in soil NO3− from almost all sites of these four deserts. There was a strong negative correlation between the mean annual precipitation (MAP) and soil NO3− Δ17O values (ΔONO3soil17). This MAP-ΔONO3soil17 correlation advocated ΔONO3soil17 as a new precipitation proxy and was then used to assess precipitation changes in southwestern US at the Pliocene–Pleistocene boundary, in South America during the Miocene, and the Sahara Desert in the past 10 kyr using NO3− Δ17O in paleosols or ancient aquifers. Global and the US maps of surface ΔONO3soil17 were also projected with available MAP datasets based on the MAP-ΔONO3soil17 model.